It is not just the £800m price tag; there is something dated and illiberal about the idea that the entire nation's cohort of 16-year-olds should be told what to do by the post-bureaucratic bureaucracy for three weeks of their summer holidays.

If you are a 16 year old which party would you want to win: a party who is pledging to give 16-year-olds the vote, or a party who is pledging to force you to do three weeks of National service during your summer holidays? Or, more pertinent to this election, if you are a sympathetic 18-year-old who would you vote for?

I think we can assign cameron's National Service to the bin of "unworkable policies".